The present invention relates to germanium semiconductor technology, and more particularly to a high quality germanium-germanium nitride interface without adverse oxygen incorporation.
The principal reason for the early demise of germanium transitor technology was the lack of a stable non-hygroscopic native insulator and the competing availability of such an insulator for silicon. Subsequent to the general replacement of germanium by silicon, several advances have been shown to provide a stable insulator for germanium.
One such advance is of a subcutaneously grown germanium dioxide insulator using a deposited silicon dioxide overlayer through which oxygen is admitted at high temperature. This work was reported by V. M. Zabotin as "Effect of a GeO.sub.2 System" published in Mikroelektronika, Vol. 6, No. 4, pp 359-364 July-August 1977. Although duplicated by others in the U.S., interface state charge densities are not as low as those of the Si/SiO.sub.2 interface and the stability of such an insulator layer is questionable.
J. Rosenberg and E. S. Yang of Columbia University have used a conventional thermal nitridation process to grow a germanium nitride insulator on germanium and to demonstrate a remarkable surface electron mobility of 1900 cm.sup.2 volt-second. This process, however, admits too much oxygen and resulted in insulators of too low resistivity to be practical. The ammonia used to grow the germanium nitride acts as an etchant which must be inhibited by a brief oxide growth. The oxide, in turn, must be later pyrolized after a sufficient Ge.sub.3 N.sub.4 overgrowth occurs. This procedure does not lead to reproducibility.
Accordingly it is desirable to provide a stable insulator for germanium.